JP2016030818A - Polystyrene-based resin composition, biaxially stretched styrenic resin sheet and molded product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide; a polystyrene-based resin composition which improves surface impact strength and heat resistance without impairing transparency and thus can be thinned and has good secondary moldability; a biaxially stretched styrenic sheet obtained using the same; and a molded product thereof.SOLUTION: There are provided: a polystyrene-based resin composition which comprises a polystyrene-based resin (A) obtained by copolymerizing monomers consisting essentially of a styrene-based monomer (a1) and methacrylic acid (a2) and inorganic fine particles (B) having an average particle diameter of 0.1 to 10 μm, wherein the blending ratio in a composition of the inorganic fine particles (B) is in the range of 0.01 to 1.0 mass%; a biaxially stretched styrenic resin sheet obtained using the same; and a molded product thereof.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a specific styrene resin composition containing inorganic fine particles, and more specifically, the strength can be improved without impairing transparency in a molded product obtained from the styrene resin composition. The present invention relates to a styrene-based resin composition that is excellent in properties and can contribute to thinning of a molded product, a sheet obtained by biaxially stretching the composition, and a molded product obtained therefrom.

  A sheet obtained from polystyrene is mainly used as a food packaging container because of its excellent transparency and rigidity. However, although the sheet container obtained from polystyrene is suitable as a general food packaging container, the sheet impact is insufficient, so the sheet is used for reducing the volume of packaging material or improving moldability. Alternatively, if it is attempted to reduce the thickness of the secondary molded product, it is difficult to maintain the suitability as a packaging material at a practical level, that is, the trade-off between strength and formability cannot be resolved, and this solution Is required.

  In addition, recently, there has been an increasing use method in which food packaging containers are heated by a microwave oven with the contents contained. However, depending on the use conditions, the container may be deformed due to insufficient heat resistance, and further improvement in heat resistance is required for food packaging containers.

  As a means for improving impact resistance, for example, a method of mixing a small amount of fine particles with a styrene resin is provided (for example, see Patent Document 1). The molded product of the styrenic resin composition substantially provided in this document is an injection molded product, which improves impact strength in practical use in the injection molded product, but is processed into a sheet shape. There is no description as to whether or not the impact strength is improved.

  On the other hand, in order to improve anisotropy when processed into a film, it has been proposed to blend specific fine particles with a styrenic resin (see, for example, Patent Document 2). In this document, the improvement effect of anisotropy when an inflation film is used is shown, but the tensile strength in the MD direction (film winding direction) is rather lowered when fine particles are added. However, it is clear that the mechanical strength is not improved by adding fine particles to the styrene resin.

  In addition, for the purpose of improving impact strength while maintaining transparency, a molded body in which a small amount of fine particles are mixed and stretched has been proposed (for example, see Patent Document 3). Although this document shows an effect of improving impact strength, there is no description about heat resistance.

JP 07-228737 A JP 2000-044745 A JP 07-323474 A

  In view of these circumstances, the problem to be solved by the present invention is to improve the surface impact strength and heat resistance without impairing the transparency, and thus can be thinned and has good secondary moldability. It is in providing the composition, the biaxially-stretched styrene-type sheet | seat obtained using this, and its molded article.

  As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by using a specific styrene-based resin composition containing a specific amount of inorganic fine particles. It came to complete.

  That is, the present invention relates to a styrene resin (A) obtained by copolymerizing monomers essential to the styrene monomer (a1) and methacrylic acid (a2), and an average particle size of 0.1 to 10 μm. A styrene-based resin composition characterized in that the blending ratio of the inorganic fine particles (B) in the composition is in the range of 0.01 to 1.0% by mass. The present invention provides a biaxially stretched sheet and a molded product.

  The styrenic resin composition of the present invention improves the heat resistance of the composition by copolymerizing a specific monomer, and particularly when processed into a sheet by blending specific fine particles. Impact strength can be improved. For this reason, the heat resistance and impact strength of the molded product are improved without sacrificing the transparency inherent in the styrene-based resin, making it possible to reduce the thickness and improving the secondary moldability, making it suitable as a packaging material for food applications, etc. Can be used.

It is the chromatograph which measured molecular weight by GPC-MALLS. It is a simplified apparatus figure for carrying out continuous block polymerization of a styrene resin composition.

Hereinafter, the composition of the present invention will be described in detail.
[Styrene resin composition]
The styrene resin composition used in the present invention has a styrene resin (A) obtained by copolymerizing monomers having styrene monomer (a1) and methacrylic acid (a2) as essential components, and an average particle size. It is a styrene resin composition containing 0.1 to 10 μm of inorganic fine particles (B), and the blending ratio of the inorganic fine particles (B) in the composition is in the range of 0.01 to 1.0% by mass. It is characterized by.

  Examples of the styrene monomer (a1) include the following. Styrene and its derivatives; for example, styrene, methyl styrene, dimethyl styrene, trimethyl styrene, ethyl styrene, diethyl styrene, triethyl styrene, propyl styrene, butyl styrene, hexyl styrene, heptyl styrene, alkyl styrene such as octyl styrene, fluorostyrene, chlorostyrene , Halogenated styrene such as bromostyrene, dibromostyrene and iodostyrene, nitrostyrene, acetylstyrene, methoxystyrene and the like, which can be used alone or in combination of two or more. Further, together with the styrene monomer (a1), a compound copolymerizable with the styrene monomer (a1), for example, vinyl monomers such as ester derivatives such as acrylonitrile, methacrylonitrile, methyl methacrylate, butyl acrylate, and the like Maleic acid, maleimide, nucleus-substituted maleimide and the like may be used in combination.

  In addition to the above, in the styrene resin, so-called impact-resistant polystyrene (HIPS) obtained by adding a butadiene rubber component during polymerization and grafting may be mixed.

  Furthermore, in addition to the styrene monomer (a1) and methacrylic acid (a2), a multi-branched macromonomer (a3) having a plurality of branches and a plurality of polymerizable double bonds is copolymerized. Styrenic resin containing a multi-branched copolymer obtained by the above may be used. Alternatively, this multi-branched copolymer may be mixed with the copolymer described above.

  When a copolymer of styrene monomer (a1) and methacrylic acid (a2) is used, a sheet having excellent heat resistance can be obtained, so that a molded product that can be used as a food packaging material using a microwave oven or the like is obtained. It is done.

  At this time, as a use ratio of the styrene monomer (a1) and methacrylic acid (a2), from the viewpoint of heat resistance and moldability of the molded product, as a mass ratio represented by (a1) / (a2), The range is preferably 99.9 / 0.1 to 97.0 / 3.0% by mass.

  In addition, when the multi-branched macromonomer (a3) having a plurality of branches and having a plurality of polymerizable double bonds is used in combination, it is possible to increase the molecular weight of the styrene resin (A). As a result, the mechanical strength of the obtained molded product can be improved. As a result, it is preferable that the sheet obtained from the resin composition and the secondary molded product thereof be used together in that the thickness can be reduced.

  Accordingly, the styrenic resin (A) comprises a styrenic monomer (a1), methacrylic acid (a2), a multi-branched macromonomer (a3) having a plurality of branches and a plurality of polymerizable double bonds. And a monomer obtained by copolymerizing the monomers essential to styrene), and the ratio of the styrene monomer (a1) and the methacrylic acid (a2) used is (a1) / The mass ratio represented by (a2) is more preferably in the range of 99.9 / 0.1 to 97.0 / 3.0 mass%.

  When the styrene resin (A) used in the present invention does not use a multi-branched macromonomer (a3) having a plurality of branches and a plurality of polymerizable double bonds, the weight average determined by GPC The molecular weight is preferably in the range of 100,000 to 400,000. When the multibranched macromonomer (a3) is used in combination, the weight average molecular weight determined by the GPC-MALLS method is 150,000 to 750,000. Furthermore, from the viewpoint of productivity and workability, it is more preferably in the range of 200,000 to 600,000. The styrenic resin (A) may be a single one or a mixture of a plurality of copolymers. In the case of a mixture, the molecular weight of the mixture is preferably within the above-mentioned range. . In the case of a mixture, a styrene resin (A) obtained by copolymerizing monomers having styrene monomer (a1) and methacrylic acid (a2) as essential is a resin in the styrene resin composition. Containing 85% by mass or more as a component is preferable in that the effects of the present invention are easily achieved.

[GPC-MALLS]
When the hyperbranched macromonomer (a3) is used in combination, when the molecular weight of the styrene resin (A) is measured by GPC-MALLS, for example, the chromatograph shown in FIG. 1 is obtained. In FIG. 1, the peak on the low molecular weight side is P1, and the peak on the high molecular weight side is P2. The peak P1 is presumed to contain a linear resin and a resin with a low degree of branching. The peak P2 is presumed to contain mainly a multi-branched resin having a high degree of branching. The region of peak P2 includes a perpendicular line drawn from the highest point of peak P2 to the baseline (a dotted line drawn substantially parallel to the volume axis in FIG. 1), a baseline, and a molecular weight curve on the left side from the highest point. And a molecular weight curve formed when the region (1) is folded to the right side with the perpendicular as the axis of symmetry (in FIG. 1, a virtual line indicated by a dotted line on the right side of the perpendicular). This is a region formed by a region (2) surrounded by a molecular weight curve), a perpendicular, and a base line. The region of peak P1 is a portion obtained by subtracting the region of peak P1 composed of the region (1) and region (2) from the region surrounded by the molecular weight curve and the baseline.

[Blend ratio of resin in peak P1 region and resin in peak P2 region]
When the multi-branched macromonomer (a3) is used in combination, the mass ratio of the resin in the peak P1 region and the resin in the peak P2 region of the styrenic resin (A) depends on the strength and workability of the resulting sheet. (Resin in the region of peak P2) / (resin in the region of peak P1) = 30/70 to 70/30 is preferable, and 40/60 to 60/40 is more preferable. This ratio can be adjusted by adjusting the ratio of the multi-branched macromonomer (a3) and the styrene monomer (a1), methacrylic acid (a2), or other monomers used in combination as necessary, It can be easily controlled by the type and the amount of use.

[Multi-branched macromonomer (a3)]
As the multi-branched macromonomer (a3) having a plurality of branches and having a plurality of polymerizable double bonds that can be used in the present invention, from the viewpoint of suppressing the generation of gel and ensuring fluidity. The multi-branched macromonomer (a3) has a weight average molecular weight (Mw) of preferably 1,000 to 15,000, more preferably 3,000 to 8,000.

  The branched structure in the multi-branched macromonomer (a3) is not particularly limited, but all three bonds other than the electron-withdrawing group and the bond that is bonded to the electron-withdrawing group are bonded to the carbon atom 4 Those that are branched by secondary carbon atoms and those that form a branched structure by repeating structural units having an ether bond, an ester bond or an amide bond are preferred.

  When the hyperbranched macromonomer (a3) forms a branched structure with the quaternary carbon, the electron withdrawing group content is 2.5 × 10 5 per g of the hyperbranched macromonomer (a3). It is preferably in the range of −4 mmol to 5.0 × 10 −1 mmol, more preferably in the range of 5.0 × 10 −4 mmol to 5.0 × 10 −2 mmol.

  It is essential that the multi-branched macromonomer (a3) has two or more polymerizable double bonds per molecule. As content of the said polymerizable double bond, it is preferable that it is the range of 0.1-5.5 mmol per 1 g of this macromonomer (a3), More preferably, it is the range of 0.5-3.5 mmol. The polymerizable double bond is preferably present at the tip of the multi-branched macromonomer (a3).

  The multi-branched macromonomer (a3) that can be used in the present invention includes a branched structure formed by repeating structural units having an ester bond, an ether bond or an amide bond, and two or more polymerizable groups in one molecule at the branch end. A multi-branched macromonomer (a3-i) having a double bond can be mentioned.

  In the multibranched macromonomer (a3-i-1) in which a structural unit having an ester bond is repeatedly formed to form a branched structure, the carbon atom adjacent to the carbonyl group of the ester bond forming the molecular chain is a quaternary carbon atom. A preferred embodiment is one in which a polymerizable double bond such as a vinyl group or an isopropenyl group is introduced into a multi-branched polyester polyol. Introducing a polymerizable double bond into a multi-branched polyester polyol can be carried out by an esterification reaction or an addition reaction.

  In the multi-branched polyester polyol, a substituent may be introduced into a part of the hydroxy group in advance by an ether bond or other bond, and a part of the hydroxy group may be oxidized or other reaction. It may be denatured. Further, in the hyperbranched polyester polyol, a part of the hydroxy group may be esterified in advance.

  Examples of the multi-branched macromonomer (a3-i-1) include a compound having one or more hydroxy groups, a carbon atom adjacent to the carboxy group being a quaternary carbon atom, and two or more hydroxy groups. It is obtained by reacting a monocarboxylic acid having a multi-branched polymer, and then reacting the hydroxyl group, which is a terminal group of the polymer, with an unsaturated acid such as acrylic acid or methacrylic acid or an acrylic compound containing an isocyanate group. Things. In addition, about the multibranched polymer which formed the branched structure by repeating the structural unit which has an ester bond, "Angew.Chem.Int.Ed.Engl.29" p138-177 (1990) by Mr. Tamalia etc. Have been described.

  Examples of the compound having at least one hydroxy group include a) aliphatic diol, alicyclic diol, or aromatic diol, b) triol, c) tetraol, d) sugar alcohols such as sorbitol and mannitol, e) anne Hydroenenea-heptitol or dipentaerythritol, f) α-alkyl glucoside such as α-methyl glycoside, g) monofunctional alcohol such as ethanol, hexanol, h) alkylene oxide having a weight average molecular weight of at most 8,000, or The hydroxy group containing polymer etc. which were produced | generated by making the derivative and the hydroxyl group in 1 or more types of compounds selected from any of said a) -g) react can be mentioned.

  Examples of the a) aliphatic diol, alicyclic diol and aromatic diol include, for example, 1,2-ethanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1, 6-hexanediol, polytetrahydrofuran, dimethylolpropane, neopentylpropane, 2-propyl-2-ethyl-1,3-propanediol, 1,2-propanediol, 1,3-butanediol, diethylene glycol, triethylene glycol , Polyethylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol; cyclohexanedimethanol, 1,3-dioxane-5,5-dimethanol; 1,4-xylylenediethanol, 1-phenyl-1,2-ethanediol Etc. . Examples of the b) triol include trimethylolpropane, trimethylolethane, trimethylolbutane, glycerol, 1,2,5-hexanetriol, 1,3,5-trihydroxybenzene, and the like. Examples of c) tetraol include pentaerythritol, ditrimethylolpropane, diglycerol, and ditrimethylolethane.

  Examples of the monocarboxylic acid in which the carbon atom adjacent to the carboxyl group is a quaternary carbon atom and having two or more hydroxy groups include, for example, dimethylolpropionic acid, α, α-bis (hydroxymethyl) butyric acid, α , Α, α-tris (hydroxymethyl) acetic acid, α, α-bis (hydroxymethyl) valeric acid, α, α-bis (hydroxymethyl) propionic acid, and the like. By using the monocarboxylic acid, the ester decomposition reaction is suppressed and a multibranched polyester polyol can be formed.

  Further, it is preferable to use a catalyst when producing the multi-branched polyester polyol. Examples of the catalyst include organic tins such as dialkyltin oxide, halogenated dialkyltin, dialkyltin biscarboxylate, and stannoxane. Examples thereof include compounds, titanates such as tetrabutyl titanate, organic sulfonic acids such as Lewis acid and p-toluenesulfonic acid.

  As the multi-branched macromonomer (a3-i-2) in which a structural unit having an ether bond is repeated to form a branched structure, for example, one hydroxy group is added to a compound having one or more hydroxy groups or cyclic ether compounds. By reacting the cyclic ether compound having the above, a multi-branched polymer is obtained, and then an unsaturated acid such as acrylic acid or methacrylic acid, an isocyanate group-containing acrylic compound, 4-chloromethyl is added to the hydroxy group which is a terminal group of the polymer. Examples thereof include those obtained by reacting halogenated methylstyrene such as styrene. Further, as a method for producing the multi-branched polymer, a compound containing one or more hydroxy groups and two or more hydroxy groups and a halogen atom, -OSO2OCH3 or -OSO2CH3, based on Williamson's ether synthesis method A method of reacting with is also useful.

  As the compound having one or more hydroxy groups, any of those mentioned above can be used, and as the cyclic ether compound having one or more hydroxy groups, for example, 3-ethyl-3- (hydroxymethyl) Examples include oxetane, 2,3-epoxy-1-propanol, 2,3-epoxy-1-butanol, and 3,4-epoxy-1-butanol. The compounds having one or more hydroxy groups used in the Williamson ether synthesis method may be those described above, but aromatic compounds having two or more hydroxy groups bonded to an aromatic ring are preferred. Examples of the compound include 1,3,5-trihydroxybenzene, 1,4-xylylenediethanol, 1-phenyl-1,2-ethanediol and the like. Examples of the compound containing two or more hydroxy groups and a halogen atom, —OSO 2 OCH 3 or —OSO 2 CH 3 include 5- (bromomethyl) -1,3-dihydroxybenzene, 2-ethyl-2- (bromomethyl) -1 , 3-propanediol, 2-methyl-2- (bromomethyl) -1,3-propanediol, 2- (bromomethyl) -2- (hydroxymethyl) -1,3-propanediol, and the like. In addition, when manufacturing the said multi-branched polymer, it is preferable to use a catalyst normally, and examples of the catalyst include BF3 diethyl ether, FSO3H, ClSO3H, and HClO4.

  In addition, examples of the multibranched macromonomer (a3-i-3) in which a structural unit having an amide bond is repeated to form a branched structure include those having an amide bond in the molecule through a nitrogen atom in the molecule. A typical example is the generation 2.0 (PAMAM dentrimer) manufactured by Dentorite.

[Polymerization method of hyperbranched macromonomer (a3), styrene monomer (a1), methacrylic acid (a2)]
When the hyperbranched macromonomer (a3), the styrene monomer (a1), and methacrylic acid (a2) are copolymerized with other monomers used in combination as necessary, a hyperbranched resin and polymerization conditions are obtained. To obtain a resin mixture which is a mixture of a linear resin and a low-branched resin produced simultaneously. At this time, the above-mentioned multibranched macromonomer (a3) is preferably used in a ratio of 50 ppm to 1%, more preferably 100 ppm to 3000 ppm (mass basis) with respect to the total amount of other monomers. It is easy to produce a branched resin and facilitates the production of the styrene resin (A) used in the present invention.

  Various commonly used polymerization methods of styrene monomers can be applied to the polymerization reaction. The polymerization method is not particularly limited, but bulk polymerization, suspension polymerization, or solution polymerization is preferable. Among them, continuous bulk polymerization is particularly preferable from the viewpoint of production efficiency.For example, by performing continuous bulk polymerization incorporating one or more stirred reactors and a tubular reactor in which a plurality of mixing elements having no moving parts are fixed. An excellent resin can be obtained. Although thermal polymerization can be performed without using a polymerization initiator, it is preferable to use various radical polymerization initiators. Moreover, what is used for manufacture of a normal polystyrene can be used for polymerization adjuvants, such as a suspending agent and an emulsifier required for superposition | polymerization.

  In order to reduce the viscosity of the reaction product in the polymerization reaction, an organic solvent may be added to the reaction system. Examples of the organic solvent include toluene, ethylbenzene, xylene, acetonitrile, benzene, chlorobenzene, dichlorobenzene, and anisole. , Cyanobenzene, dimethylformamide, N, N-dimethylacetamide, methyl ethyl ketone and the like. In particular, when it is desired to increase the amount of the hyperbranched macromonomer, it is preferable to use an organic solvent from the viewpoint of suppressing gelation. Thereby, the addition amount of the multibranched macromonomer (a3) shown above can be dramatically increased to introduce a lot of branched structures, and gelation hardly occurs.

  The radical polymerization initiator is not particularly limited. For example, 1,1-bis (t-butylperoxy) cyclohexane, 2,2-bis (t-butylperoxy) butane, 2,2-bis (4 , 4-di-butylperoxycyclohexyl) propane and other peroxyketals, cumene hydroperoxide, hydroperoxides such as t-butyl hydroperoxide, di-t-butyl peroxide, dicumyl peroxide, di Dialkyl peroxides such as -t-hexyl peroxide, diacyl peroxides such as benzoyl peroxide and disinamoyl peroxide, t-butyl peroxybenzoate, di-t-butyl peroxyisophthalate, t-butyl peroxide Pao such as oxyisylpropyl monocarbonate Siesters, N, N′-azobisisobutylnitrile, N, N′-azobis (cyclohexane-1-carbonitrile), N, N′-azobis (2-methylbutyronitrile), N, N′-azobis ( 2,4-dimethylvaleronitrile), N, N′-azobis [2- (hydroxymethyl) propionitrile] and the like, and these can be used alone or in combination.

  Furthermore, you may add a chain transfer agent so that the molecular weight of the resin composition obtained may not become too large. As the chain transfer agent, either a monofunctional chain transfer agent having one chain transfer group or a polyfunctional chain transfer agent having a plurality of chain transfer groups can be used. Examples of the monofunctional chain transfer agent include alkyl mercaptans and thioglycolic acid esters. Polyfunctional chain transfer agents include ethylene glycol, neopentyl glycol, trimethylol propane, pentaerythritol, dipentaerythritol, tripentaerythritol, sorbitol and the like, the hydroxy group in thioglycolic acid or 3-mercaptopropionic acid And the like esterified with.

  In addition, long chain alcohols, polyoxyethylene alkyl ethers, polyoxyethylene lauryl ethers, polyoxyoleyl ethers, polyoxyethylene alkenyl ethers, and the like can be used to suppress gel formation in the resin composition obtained. .

  In addition, a lubricant, an antistatic agent, an antioxidant, a heat stabilizer, an ultraviolet absorber, a dye, a plasticizer, and the like can be used as long as the physical properties of the obtained resin composition and sheet are not impaired.

<Polymerization process>
In the polymerization step, the styrenic monomer (a1), methacrylic acid (a2), other monomers used in combination, and the multi-branched macromonomer (a3) are used as monomers, and these are copolymerized to produce a styrenic resin ( A) can be obtained. An example of the reaction vessel of the polymerization apparatus for obtaining the resin (A) in the present invention is shown in FIG. That is, the reaction solution is sent to the stirring reactor (I) by the pump (1), then sent to the circulation polymerization line (II) by the pump (2), and the inside of the circulation polymerization line (II) is sent by the pump (3). It circulates, and after circulation, it is sent to the non-circulation polymerization line (III). Here, the circulation polymerization line (II) is composed of three reactors composed of (4) to (6), and the non-circulation polymerization line (III) is composed of three reactors composed of (7) to (9). Is done.

  If necessary, add monomers and solvents between the stirred reactor (I) and the circulation polymerization line (II), or between the circulation polymerization line (II) and the non-circulation polymerization line (III). It is also possible to add.

<Devolatile process>
After the polymerization step, a devolatilization tank 1 and a devolatilization tank 2 for volatilizing unreacted monomers and solvent components are connected. The devolatilization tank 1 and the devolatilization tank 2 are preferably adjusted to a reduced pressure of 4.0 kPa and 1.3 kPa, respectively, and after passing through the devolatilization tank 1 and the devolatilization tank 2, they are pelletized. The styrene resin (A) to be used can be obtained.

<Inorganic fine particles (B)>
In the present invention, the inorganic fine particles (B) are used in the composition in a range of 0.01 to 1.0% by mass with respect to the above-mentioned styrenic resin (A).

  It is essential that the average particle size of the inorganic fine particles (B) is in the range of 0.1 to 10 μm. In the present invention, the average particle diameter is a value determined by a laser diffraction method, and when it is not a perfect spherical particle, it is the average value of the longest part of the primary particles.

  When the average particle size is less than 0.1 μm, the surface impact strength of the sheet obtained using this composition does not reach a practical level, and when it exceeds 10 μm, the molded product obtained is obtained. Insufficient transparency.

  Examples of the inorganic fine particles (B) include, for example, barium sulfate, talc, calcium phosphate and the like, and in particular, barium sulfate does not impair the transparency in a molded product and contributes to improvement of mechanical strength. It can be preferably used.

  Further, the inorganic fine particles (B) preferably have an average particle diameter of 0.5 to 8 μm, and the shape thereof is preferably a plate shape. As inorganic fine particles marketed as having such an average particle diameter, Sakai Chemical Industry Co., Ltd., plate-like barium sulfate A and the like can be mentioned.

  Moreover, as the use ratio, from the viewpoint of excellent balance between the surface impact strength and transparency of the obtained molded product, it is essential that it is in the range of 0.01 to 1.0% by mass, The range is preferably 0.5% by mass.

<Method for Preparing Styrenic Resin Composition>
The styrenic resin composition in the present invention can be produced by the following method. A method in which a styrene monomer (a1), a methacrylic acid (a2), a monomer that can be copolymerized with a styrene monomer that is used together if necessary, and inorganic fine particles (B) are uniformly mixed in advance, and the mixed solution is polymerized; Alternatively, a method of adding the inorganic fine particles (B) to the polymerization solution of the styrene resin (A) or a method of adding the inorganic fine particles (B) to the melt of the styrene resin (A) can be mentioned. When the inorganic fine particles (B) are added to the melt of the styrenic resin (A), it can be prepared by melt-kneading with a twin screw extruder or the like. It is also possible to prepare a master batch by melt-kneading to a concentration, and then diluting with a styrene resin (A) to a specified concentration by melt-kneading.

<Unstretched sheet>
The non-stretched sheet can be produced by melting and extruding pellets of the styrene-based resin composition obtained above with an extruder and then melt-extruding them into a sheet with a T-die, and then cooling them with a cooling roll or the like. As a cooling temperature, 70-90 degreeC is preferable.

<Biaxially stretched sheet>
The biaxially stretched sheet is obtained by stretching in a longitudinal and lateral biaxial direction with a stretching machine after melt extrusion with an extruder. For example, first, a heat-resistant styrenic resin composition is supplied to an extruder and melt-extruded into a sheet form from a T-die. At that time, casting is performed so that the sheet before stretching has a predetermined thickness. Thereafter, the sheet is cooled to a temperature capable of biaxial stretching, for example, 110 to 145 ° C., and stretched in the longitudinal direction (flow direction) and the transverse direction (cross direction with respect to the flow direction).

  As the stretching method, simultaneous biaxial stretching or sequential biaxial stretching can be performed after the styrenic resin composition is melt extruded and formed into a sheet. In the case of sequential biaxial stretching, it is common to first perform longitudinal stretching and then perform lateral stretching. In particular, in a biaxially stretched styrene-based sheet, a longitudinal stretching using a roll is followed by a lateral stretching using a tenter. The tenter method is advantageous in that a wide range of products can be obtained and productivity is high.

  As a longitudinal stretching method using a roll, a low-speed roll and a high-speed roll are rotated in the same direction to pass the resin flat, and a stretching method, and a low-speed roll and a high-speed roll are rotated in reverse to pass the resin through the cloth. There is a method of paper and drawing, and any combination of single-stage or multi-stage, flat or cross can be used.

  As specific stretching conditions, the stretching ratio varies depending on the purpose, but is usually 1.5 to 15 times, more preferably 4 to 10 times in terms of surface magnification. In the case of sequential stretching, the draw ratio in the flow direction is 1.2 to 5 times, preferably 1.5 to 3.0 times, and the draw ratio in the cross direction with respect to the flow direction is 1.2 to 5 times. The ratio is preferably 1.5 to 3.0 times. The draw ratio in each direction of simultaneous biaxial stretching is 1.5 to 5 times. Further, the temperature condition at this time is preferably such that the orientation relaxation stress measured according to ASTM D-1504 is 0.2 to 2.0 MPa, more preferably 0.4 to 1.0 MPa. If the orientation relaxation stress is less than 0.2 MPa, the impact resistance of the sheet is likely to be insufficient, and if it exceeds 2.0 MPa, the sheet is likely to be stretched and the secondary formability may be poor. Because there is. On the other hand, the range of 0.4 to 1.0 MPa is more preferable because not only the crackability of the obtained sheet is good, but also the formability of the sheet itself is extremely good.

  In this case, for example, the unstretched raw sheet is stretched in the longitudinal direction at a stretching temperature of 110 to 145 ° C. at the above magnification, and then crossed with respect to the longitudinal direction at a stretching temperature of 110 to 145 ° C. Stretching is performed in the direction at the above magnification.

  The thickness of the biaxially stretched sheet made of the styrene resin composition is preferably 0.1 to 0.5 mm. The biaxially stretched sheet may be laminated with the same or different thermoplastic resin by coextrusion or dry lamination, if necessary. Moreover, you may apply | coat an antifogging agent etc. to the said biaxially stretched sheet as needed.

  The obtained biaxially stretched sheet can be easily obtained in a desired container, lid, and the like if it is pressure-formed with a mold having a predetermined shape under the same conditions as those of a conventional biaxially stretched polystyrene sheet.

  Hereinafter, the present invention will be described more specifically with reference to examples. The present invention should not be limited to the scope of these examples. Hereinafter, “part” and “%” are based on mass unless otherwise specified.

[GPC-MALLS measurement]
GPC-MALS measurement of the styrene-based resin composition was performed under the conditions of Shodex HPLC, detector Wyatt Technology DAWN EOS, Shodex RI-101, column Shodex KF-806L × 2, solvent THF, and flow rate of 1.0 ml / min. . In addition, the analysis of the measurement of GPC-MALLS was performed by analysis software ASTRA manufactured by Wyatt, and the weight average molecular weight was obtained for the styrene resin composition, and the molecular weight of the resin composition obtained from GPC-MALLS was plotted on the horizontal axis. The slope in the region of molecular weight 250,000 to 10 million in the logarithmic graph with the radius of inertia as the vertical axis (automatically calculated by the software based on the measured value of only the linear portion obtained in the molecular weight range) The slope of the approximate line was determined.

[Melt Mass Flow Rate Measurement Method]
The measurement was performed according to JIS K7210. The measurement conditions are 230 ° C. and 37N.

[Measurement method of Vicat softening temperature]
The measurement was performed according to JIS K7206.

[Melting and sheeting of styrene resin and inorganic fine particles]
Styrenic resin (A) and inorganic fine particles (B) were previously mixed at a mass ratio of 97.0 / 3.0, and melt-kneaded at 230 ° C. using a twin screw extruder to prepare a master batch. Next, the styrene-based resin (A) and the master batch are preliminarily mixed at a mass ratio of 90/10, and the extrusion temperature is 230 ° C., the roll temperature is 85 ° C., and the take-off speed is 0.8 to 0.00 using a 40 mm single screw extruder. A sheet having a thickness of 1.0 mm was formed at 9 m / min.

[Sheet stretching process]
The obtained sheet was cut into 8 × 8 cm and stretched 2.5 times at a stretching temperature of 130 ° C. using a single stretcher to obtain a stretched sheet.

[Evaluation of impact strength of sheet]
After producing a stretched sheet using a styrene-based resin composition, impact strength was measured using a dirt impact tester manufactured by Toyo Seiki Co., Ltd.

[Sheet transparency evaluation]
Haze (turbidity) was measured according to JIS K7105.

Reference Example 1 Synthesis of Multibranched Macromonomer (Mm-1) <Synthesis of Multibranched Polyether Polyol 1>
To a 2 liter flask equipped with a stirrer, thermometer, dropping funnel and condenser, 50.5 g of ethoxylated pentaerythritol (5 mol-ethylene oxide-added pentaerythritol) and 1 g of BF 3 diethyl ether solution (50%) were added at room temperature, and 110 Heated to ° C. To this, 450 g of 3-ethyl-3- (hydroxymethyl) oxetane was slowly added over 25 minutes while controlling the exotherm due to the reaction. When the exotherm had subsided, the reaction mixture was further stirred at 120 ° C. for 3 hours and then cooled to room temperature. The resulting multi-branched polyether polyol had a weight average molecular weight of 3,000 and a hydroxyl value of 530.

<Synthesis of Multibranched Polyether 1 Having Methacryloyl Group and Acetyl Group>
In a reactor equipped with a Dean-Stark decanter equipped with a stirrer, a thermometer, a condenser, and a gas introduction tube, 50 g of the multi-branched polyether polyol obtained in the above-mentioned <Synthesis of multi-branched polyether polyol 1>, methacrylic acid 13 .8 g, 150 g of toluene, 0.06 g of hydroquinone and 1 g of paratoluenesulfonic acid, and stirring under normal pressure while blowing 7% oxygen-containing nitrogen (v / v) into the mixed solution at a rate of 3 ml / min. Heated. The amount of heating was adjusted so that the amount of distillate in the decanter was 30 g per hour, and heating was continued until the amount of dehydration reached 2.9 g. After completion of the reaction, the mixture was cooled once, 36 g of acetic anhydride and 5.7 g of sulfamic acid were added, and the mixture was stirred at 60 ° C. for 10 hours. Thereafter, in order to remove the remaining acetic acid and hydroquinone, it was washed with 50 g of 5% aqueous sodium hydroxide solution four times, and further washed once with 50 g of 1% aqueous sulfuric acid solution and twice with 50 g of water. To the obtained organic layer, 0.02 g of methoquinone was added, the solvent was distilled off while introducing 7% oxygen-containing nitrogen (v / v) under reduced pressure, and 60 g of a multibranched polyether having an isopropenyl group and an acetyl group was obtained. Obtained. The weight average molecular weight of the obtained multibranched polyether was 3,900, and the introduction ratios of isopropenyl group and acetyl group into the multibranched polyether polyol were 30 mol% and 62 mol%, respectively.

Reference Example 2 Synthesis of Multibranched Macromonomer (Mm-2) <Synthesis of Multibranched Polyether Polyol 2>
In a 1000 mL three-necked flask connected with nitrogen, air reflux condenser, magnetic stir bar and thermometer, 1.24 g (8.7 mmol) of boron trifluoride diethyl ether complex was dried and the peroxide was removed. Dilute with 273 g of methyl-t-butyl ether. In a separate container, 140 g (1.21 mol) of 3-hydroxymethyl-3-ethyloxetane and 70.0 g (1.21 mol) of propylene oxide were mixed, and the above three-necked flask was consumed with a metering pump for 5.5 hours. And dripped. At this time, the system was cooled by an ice bath as needed to keep the temperature in the system at 20 ° C. After completion of the dropwise addition, 63.0 g (1.08 mol) of propylene oxide was further added dropwise over 3 hours while keeping the temperature in the system at 20 ° C., and the mixture was further stirred for 4 hours. Here, 0.620 g (4.4 mmol) of boron trifluoride diethyl ether complex was added, and the mixture was further stirred at 20 ° C. for 6 hours. The reaction mixture was adsorbed and removed by adding hydrotalcite 10 times the weight of boron trifluoride diethyl ether complex used in the reaction and refluxing for 1 hour. After the hydrotalcite was filtered off, methyl-t-butyl ether was removed to obtain 267 g of a transparent and highly viscous multi-branched polyether polyol. This multi-branched polyether polyol has Mn = 2,876 g / mol, Mw = 7,171 g / mol, hydroxyl value = 253 mg · KOH / g, and 3-hydroxymethyl-3-ethyl on a molar basis from proton NMR. Oxetane: propylene oxide = 1: 1.9.

<Synthesis of multi-branched polyether 2 having acryloyl group>
In a 500 mL four-necked flask equipped with a Dean-Stark tube, nitrogen and air introduction tube, a stirrer, and a thermometer, the multi-branched polyether polyol obtained in the above <Synthesis of multi-branched polyether polyol 2> 155 g, 51 g of acrylic acid, 200 g of cyclohexane, 0.21 g of hydroquinone monomethyl ether, and 4 g (12.3 mmol) of dodecylbenzenesulfonic acid as a catalyst were added, and the temperature was raised to 82 ° C. under a mixed gas flow of nitrogen and air 2 to 1. . Cyclohexane reflux began, and water flow began gradually. Thereafter, when the temperature was raised to 85 ° C. and reacted for 18 hours, 60% of the theoretical dehydration amount was reached, so cooling was started. After cooling to around 30 ° C., 5% sodium hydroxide aqueous solution and 15% NaCl aqueous solution were added for washing. The hydroxyl group value of the obtained polymerizable unsaturated group-containing multi-branched polyether was 70 mg · KOH / g, and the acrylic group introduction rate of all hydroxyl groups was 60%.

Reference Example 3 Synthesis of Multibranched Macromonomer (Mm-3) <Synthesis of Multibranched Polyether 1 Having Styryl Group and Acetyl Group>
In a reactor equipped with a stirrer, a condenser equipped with a drying tube, a dropping funnel and a thermometer, 50 g of the multibranched polyether polyol obtained in the above-mentioned <Synthesis of multibranched polyether polyol 1>, 100 g of tetrahydrofuran and sodium hydride 4.3 g was added and stirred at room temperature. To this was added dropwise 26.7 g of 4-chloromethylstyrene over 1 hour, and the resulting reaction mixture was further stirred at 50 ° C. for 4 hours. After completion of the reaction, the reaction mixture was once cooled, 34 g of acetic anhydride and 5.4 g of sulfamic acid were added, and the mixture was stirred at 60 ° C. for 10 hours. Thereafter, the tetrahydrofuran was distilled off under reduced pressure, the resulting mixture was dissolved in 150 g of toluene, washed with 50 g of 5% aqueous sodium hydroxide solution to remove the remaining acetic acid, and further 50 g of 1% aqueous sulfuric acid solution. And once with 50 g of water. The solvent was distilled off from the obtained organic layer under reduced pressure to obtain 70 g of a multi-branched polyether having a styryl group and an acetyl group. The obtained multi-branched polyether had a mass average molecular weight of 4,800, and the styryl group and acetyl group introduction rates into the multi-branched polyether polyol were 38 mol% and 57 mol%, respectively.

Reference Example 4 Synthesis of Multibranched Macromonomer (Mm-4) <Synthesis of Multibranched Macromonomer Having Methacryloyl Group and Acetyl Group>
A four-necked flask was equipped with a stirrer, pressure gauge, condenser and saucer, to which 308.9 g of ethoxylated pentaerythritol and 0.46 g of sulfuric acid were added. Then, it heated to 140 degreeC and 460.5g of 2, 2- di (hydroxymethyl) propionic acid was added over 10 minutes. After 2,2-di (hydroxymethyl) propionic acid is completely dissolved and becomes a transparent solution, the pressure is reduced to 30 to 40 mmHg and the reaction is continued for 4 hours while stirring and the acid value becomes 7.0 mgKOH / g. I let you. Thereafter, 921 g of 2,2-di (hydroxymethyl) propionic acid and 0.92 g of sulfuric acid were added to the reaction solution over 15 minutes to obtain a transparent solution, and then the pressure was reduced to 30 to 40 mmHg, while stirring. The polyester polyol was obtained by reacting for a period of time. In a reaction vessel equipped with a 7% oxygen introduction tube, a thermometer, a Dean-Stark decanter equipped with a condenser, and a stirrer, 10 g of the polyester polyol produced above, 1.25 g of dibutyltin oxide, and 100 g of methyl methacrylate having an isopropenyl group And 0.05 g of hydroquinone were added, and the mixture was heated with stirring while blowing 7% oxygen at a rate of 3 ml / min. The amount of heating is adjusted so that the amount of distillate in the decanter is 15 to 20 g per hour, the distillate in the decanter is taken out every hour, and the corresponding amount of methyl methacrylate is added for 4 hours. Reacted. After completion of the reaction, methyl methacrylate was distilled off under reduced pressure, and 10 g of acetic anhydride and 2 g of sulfamic acid were added to cap the remaining hydroxy groups, followed by stirring at room temperature for 10 hours. After removing sulfamic acid by filtration and distilling off acetic anhydride and acetic acid under reduced pressure, the residue was dissolved in 70 g of ethyl acetate and washed 4 times with 20 g of 5% aqueous sodium hydroxide to remove hydroquinone. Further, it was washed twice with 20 g of a 7% aqueous sulfuric acid solution and twice with 20 g of water. To the obtained organic layer, 0.0045 g of methoquinone was added, and the solvent was distilled off while introducing 7% oxygen under reduced pressure to obtain 11 g of a hyperbranched macromonomer (Mm-3) having an isopropenyl group and an acetyl group. It was. The resulting multi-branched macromonomer (Mm-3) has a weight average molecular weight of 3,000, a number average molecular weight of 2,100, and a double bond introduction amount of 2.00 mmol / g, an isopropenyl group and an acetyl group. The introduction rates were 55 mol% and 36 mol%, respectively.

Reference Example 5 Synthesis of hyperbranched macromonomer (Mm-5) <Synthesis of PAMAM dendrimer having a styryl group>
To a reactor equipped with a stirrer, a condenser equipped with a drying tube, a dropping funnel and a thermometer, 50 g of a methanol solution (20%) of PAMAM dendrimer (Generation 2.0: manufactured by Dentritech) was added and stirred under reduced pressure. Methanol was distilled off. Subsequently, 50 g of tetrahydrofuran and 3.0 g of finely divided potassium hydroxide were added, and the mixture was stirred at room temperature. 4-chloromethylstyrene 7.0g was dripped at this over 10 minutes, and the obtained reaction mixture was further stirred at 50 degreeC for 3 hours. After completion of the reaction, the mixture was cooled and the solid was filtered, and then tetrahydrofuran was distilled off under reduced pressure to obtain 13 g of a PAMAM dendrimer having a styryl group. The resulting styryl group content of the dendrimer was 2.7 mmol / gram.

Reference Example 6 Synthesis of Multibranched Macromonomer (Mm-6) <Multibranched Polyether Polyol 2 Having Styryl Group and Acetyl Group>
A light-shielding reaction vessel equipped with a stirrer, a condenser, a light-shielding dropping funnel and a thermometer, and capable of nitrogen sealing. Under nitrogen flow, anhydrous 1,3,5-trihydroxybenzene 0.5 g, potassium carbonate 29 g, 18-crown -6 2.7 g and acetone 180 g were added, and a solution composed of 21.7 g of 5- (bromomethyl) -1,3-dihydroxybenzene and 180 g of acetone was added dropwise over 2 hours while stirring. Thereafter, the mixture was heated and refluxed with stirring until 5- (bromomethyl) -1,3-dihydroxybenzene disappeared. Thereafter, 9.0 g of 4-chloromethylstyrene was added, and the mixture was further heated and refluxed with stirring until the disappearance. Thereafter, 4 g of acetic anhydride and 0.6 g of sulfamic acid were added to the reaction mixture, and the mixture was stirred overnight at room temperature. After cooling, the solid in the reaction mixture was removed by filtration, and the solvent was distilled off under reduced pressure. The obtained mixture was dissolved in dichloromethane and washed three times with water, and then the dichloromethane solution was added dropwise to hexane to precipitate a multibranched polyether. This was filtered and dried to obtain 12 g of a multi-branched polyether polyol having a styryl group and an acetyl group. The mass average molecular weight was 3,200, and the styryl group content was 3.5 mmol / gram.

Reference Example 7 Synthesis of Multibranched Macromonomer (M-m7) <Synthesis of Multibranched Polyester Polyol Having Methacryloyl Group and Acetyl Group>
In a reaction vessel equipped with a 7% oxygen introduction tube, a thermometer, a Dean-Stark decanter equipped with a condenser, and a stirrer, 10 g of “Boltorn H20”, 1.25 g of dibutyltin oxide, and isopropenyl group as a functional group (B) 100 g of methyl methacrylate and 0.05 g of hydroquinone were added, and the mixture was heated with stirring while blowing 7% oxygen at a rate of 3 ml / min. The amount of heating is adjusted so that the amount of distillate in the decanter is 15 to 20 g per hour, the distillate in the decanter is taken out every hour, and the corresponding amount of methyl methacrylate is added for 6 hours. Reacted.

  After completion of the reaction, methyl methacrylate was distilled off under reduced pressure, and 10 g of acetic anhydride and 2 g of sulfamic acid were added to cap the remaining hydroxy groups, followed by stirring at room temperature for 10 hours. After removing sulfamic acid by filtration and distilling off acetic anhydride and acetic acid under reduced pressure, the residue was dissolved in 70 g of ethyl acetate and washed 4 times with 20 g of 5% aqueous sodium hydroxide to remove hydroquinone. Further, it was washed twice with 20 g of a 7% aqueous sulfuric acid solution and twice with 20 g of water. To the obtained organic layer, 0.0045 g of methoquinone was added, and the solvent was distilled off while introducing 7% oxygen under reduced pressure to obtain 12 g of a hyperbranched polyester having an isopropenyl group and an acetyl group. The obtained multibranched polyester had a mass average molecular weight of 2860 and a number average molecular weight of 3770, and the introduction rates of isopropenyl group and acetyl group into the multibranched polyester polyol (A) were 55% and 40%, respectively.

Example 1
A mixed solution consisting of 98 parts of styrene monomer, 2 parts of methacrylic acid and 12 parts of toluene was prepared, and 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane was further used as the organic peroxide. 750 ppm was added to the total amount of styrene monomer and methacrylic acid, and continuous polymerization was performed under the following conditions using the apparatus shown in FIG. The stirring reactor (I) was 110 to 130 ° C., and the circulation polymerization line (II) and the non-circulation polymerization line (III) were 120 to 160 ° C., respectively. From the reaction solution, unreacted monomers and solvent components are recovered in the devolatilization tank 1 and the devolatilization tank 2 installed after the non-recycling polymerization line (III) as the final reactor. The devolatilization tank 1 and the devolatilization tank 2 were set to 240 to 280 ° C. After that, it passed through a single tube and was stranded and pelletized with a pelletizer to obtain a styrene resin.

  The obtained styrenic resin and plate-like barium sulfate having an average particle diameter of 7 μm are melt-kneaded to prepare a master batch of 3.0% by mass of barium sulfate, and then the styrene-based resin and master batch are melt-extruded to obtain barium sulfate. A sheet containing 0.3% by mass was obtained. The obtained sheet was stretched 2.5 times with a single stretcher to obtain a stretched sheet.

Example 2
A stretched sheet was obtained in the same manner as in Example 1 except that barium sulfate was changed to 4 μm plate-like barium sulfate.

Example 3
A stretched sheet was obtained in the same manner as in Example 1 except that the barium sulfate was changed to 2 μm plate-like barium sulfate.

Example 4
A stretched sheet was obtained in the same manner as in Example 1 except that barium sulfate was changed to 0.5 μm.

Example 5
Prepare a mixed solution of 98 parts of styrene monomer, 2 parts of methacrylic acid, 500 ppm of the multi-branched macromonomer (Mm-1) obtained in Reference Example 1 and 11 parts of toluene with respect to the total amount of styrene monomer and methacrylic acid. Furthermore, 300 ppm of t-butyl peroxybenzoate as an organic peroxide was added to the total amount of styrene monomer and methacrylic acid monomer, and continuous bulk polymerization was performed under the following conditions using the apparatus shown in FIG. The stirring reactor (I) was 110 to 130 ° C., and the circulation polymerization line (II) and the non-circulation polymerization line (III) were 120 to 160 ° C., respectively. From the reaction solution, unreacted monomers and solvent components are recovered in the devolatilization tank 1 and the devolatilization tank 2 installed after the non-recycling polymerization line (III) as the final reactor. The devolatilization tank 1 and the devolatilization tank 2 were set to 240 to 280 ° C. After that, it passed through a single tube and was stranded and pelletized with a pelletizer to obtain a styrene resin. A stretched sheet was obtained in the same manner as in Example 1 except that the styrene resin was obtained.

Example 6
A stretched sheet was obtained in the same manner as in Example 5 except that the macromonomer was changed to Mm-2 obtained in Reference Example 2.

Example 7
A stretched sheet was obtained in the same manner as in Example 5 except that the macromonomer was changed to Mm-3 obtained in Reference Example 2.

Example 8
A stretched sheet was obtained in the same manner as in Example 5 except that the macromonomer was changed to Mm-4 obtained in Reference Example 2.

Example 9
A stretched sheet was obtained in the same manner as in Example 5 except that the macromonomer was changed to Mm-5 obtained in Reference Example 2.

Example 10
A stretched sheet was obtained in the same manner as in Example 5 except that the macromonomer was changed to Mm-6 obtained in Reference Example 2.

Example 11
A stretched sheet was obtained in the same manner as in Example 5 except that the macromonomer was changed to Mm-7 obtained in Reference Example 2.

Comparative Example 1
A stretched sheet was obtained in the same manner as in Example 1 except that the content of methacrylic acid was 0% by mass.

Comparative Example 2
A stretched sheet was obtained in the same manner as in Example 1 except that barium sulfate was changed to 15 μm plate-like barium sulfate.

Comparative Example 3
A stretched sheet was obtained in the same manner as in Example 1 except that barium sulfate was not used.

  The evaluation results for the stretched sheet obtained above are shown below.

Claims (11)

Styrenic resin (A) obtained by copolymerization of monomers essential to styrene monomer (a1) and methacrylic acid (a2), and inorganic fine particles (B) having an average particle size of 0.1 to 10 μm And a blending ratio of the inorganic fine particles (B) in the composition is in the range of 0.01 to 1.0% by mass. The use ratio of the styrene monomer (a1) and the methacrylic acid (a2) is 99.9 / 0.1 to 97.0 / 3.0 as a mass ratio represented by (a1) / (a2). The styrenic resin composition according to claim 1, which is in a range of The styrene resin (A) is a styrene monomer (a1), methacrylic acid (a2), a multi-branched macromonomer (a3) having a plurality of branches and a plurality of polymerizable double bonds. The styrenic resin composition according to claim 1, which is a copolymer obtained by copolymerizing monomers essential for. The use ratio of the styrene monomer (a1) and the methacrylic acid (a2) is 99.9 / 0.1 to 97.0 / 3.0 as a mass ratio represented by (a1) / (a2). The styrenic resin composition according to claim 3, which is in a range. The styrenic resin composition according to any one of claims 1 to 4, wherein the inorganic fine particles (B) are barium sulfate. The styrenic resin composition according to any one of claims 1 to 5, wherein the inorganic fine particles (B) are plate-shaped fine particles. The styrene resin composition according to any one of claims 1 to 6, wherein a blending ratio of the inorganic fine particles (B) in the composition is in a range of 0.1 to 0.5 mass%. A biaxially stretched styrene-based resin sheet obtained by biaxially stretching the styrene-based resin composition according to any one of claims 1 to 7. The biaxially oriented styrene resin sheet according to claim 8, wherein the thickness of the sheet is in the range of 0.1 to 0.5 mm. A molded body obtained by molding the biaxially stretched styrene resin sheet according to claim 8 or 9. The molded article according to claim 10, which is used as a packaging material for food.